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Summary: The ribosome-associated protein quality control (RQC) pathway acts as a translational surveillance mechanism to maintain proteostasis. In mammalian cells, the cytoplasmic RQC pathway involves nuclear export mediator factor (NEMF)-dependent recruitment of the E3 ligase Listerin to ubiquitinate ribosome-stalled nascent polypeptides on the lysine residue for degradation. However, the quality control of ribosome-stalled nuclear-encoded mitochondrial nascent polypeptides remains elusive, as these peptides can be partially imported into mitochondria through translocons, restricting accessibility to the lysine by Listerin. Here, we identify a Listerin-independent organelle-specific mitochondrial RQC pathway that acts on NEMF-mediated carboxy-terminal poly-alanine modification. In the pathway, mitochondrial proteins carrying C-end poly-Ala tails are recognized by the cytosolic E3 ligase Pirh2 and the ClpXP protease in the mitochondria, which coordinately clear ribosome-stalled mitochondrial nascent polypeptides. Defects in this elimination pathway result in NEMF-mediated aggregates and mitochondrial integrity failure, thus providing a potential molecular mechanism of the RQC pathway in mitochondrial-associated human diseases.

Dravet syndrome is an epileptic encephalopathy largely due to haploinsufficiency of the voltage-gated sodium channel Nav1.1 that is expressed primarily in GABAergic neurons. In order to distinguish the different subtypes, we used gene editing to introduce tdTomato gene into the genome of iPSCs to label the GABAergic neurons in the differentiated neuronal networks. The gene-edited cell line demonstrates normal karyotype, expresses the main pluripotency markers, and shows the presence of differentiation into the three embryonic germ layers in teratomas.

Dravet syndrome is a neurological disorder characterized by treatment-resistant polymorphic seizures, primarily caused by loss-of-function in the SCN1A gene. To develop an in vitro model of this disease, in a previously study we generated an induced pluripotent stem cell line from a 10-year-old boy carrying the NM_001165963.1:c.5768A to G (Q1923R) mutation in SCN1A. Using TALEN-mediated genome editing, we have now generated an isogenic control line in which the disease-causing mutation found in the epilepsy patient iPSCs was corrected, in order to eliminate the interference of different genetic backgrounds in future analyses.

Epilepsy is a neurological disorder, characterized by recurrent (two or more) epileptic seizures resulting from excessive and abnormal cortical neural activity.Fibroblasts were collected from a 10-year-old male with antecedent febrile seizures (PEFS+) and carrying a heterozygous A > G mutation of Nav1.1 α subunit gene. The induced USTCi001-A retained the mutation, expressed pluripotent markers, showed normal karyotype, and displayed in vitro differentiation potential toward cells of the three embryonic germ layers.

Autism spectrum disorder (ASD) is a neurological disorder with complex etiologies. In this study, urine cells were collected from a 16-year-old male with ASD and reprogrammed with the human SKOM transcription factors. The patient has a heterozygous C > T mutation of FCGR1B gene that was confirmed by sequencing analysis. The pluripotency was verified by gene expression and capacity of differentiation towards the three germ layers. This kind of iPSC will be valuable for further understanding the pathogenesis of ASD and help to develop drugs for treating ASD.